First off I have to admit to being one of the folks that enjoy the ambiance created on the ship for the couple of times there's formal nights. And I do stay "dressed" for the entire evening.
I like to think those evenings are a part of what makes a cruise vacation special.

That said, I've never seen anyone turned away from a dining room for not appearing in "suggested attire." If the cruise lines want to maintain this tradition, they should take a more active approach and put in place a dress code, rather than "suggested attire."
That's not to say they couldn't attempt to please everyone. Possibly the answer is having some public rooms or lounges onboard designated "casual" for specific evening, while others retain the "dress code" for that evening.
I did notice in our cruise docs for our Carnival cruise this weekend, it states in BOLD letters, NO T-Shirts, or Shorts in the Dining Room. However, there is no mention of blue jeans, which used to be a no no as well. Guess the trend is to more casual.
I don't mind at all for casual nights. But, personally, I'd like to see the formal nights kept in place.
Fortunately I've yet to see a cruise line document or brochure outlawing antlers!